Apache Module mod_include

Summary

This module provides a filter which will process files
before they are sent to the client. The processing is
controlled by specially formatted SGML comments, referred to as
elements. These elements allow conditional text, the
inclusion of other files or programs, as well as the setting and
printing of environment variables.

See also

Server Side Includes are implemented by the
INCLUDESfilter. If
documents containing server-side include directives are given
the extension .shtml, the following directives will make Apache
parse them and assign the resulting document the mime type of
text/html:

AddType text/html .shtml
AddOutputFilter INCLUDES .shtml

The following directive must be given for the directories
containing the shtml files (typically in a
<Directory> section,
but this directive is also valid in .htaccess files if
AllowOverrideOptions
is set):

Options +Includes

For backwards compatibility, the server-parsedhandler also activates the
INCLUDES filter. As well, Apache will activate the INCLUDES
filter for any document with mime type
text/x-server-parsed-html or
text/x-server-parsed-html3 (and the resulting
output will have the mime type text/html).

Files processed for server-side includes no longer accept
requests with PATH_INFO (trailing pathname information)
by default. You can use the AcceptPathInfo directive to
configure the server to accept requests with PATH_INFO.

The document is parsed as an HTML document, with special
commands embedded as SGML comments. A command has the syntax:

<!--#elementattribute=valueattribute=value ... -->

The value will often be enclosed in double quotes, but single
quotes (') and backticks (`) are also
possible. Many commands only allow a single attribute-value pair.
Note that the comment terminator (-->) should be
preceded by whitespace to ensure that it isn't considered part of
an SSI token. Note that the leading <!--# is one
token and may not contain any whitespaces.

This command controls various aspects of the parsing. The
valid attributes are:

echomsg (Apache 2.1 and later)

The value is a message that is sent back to the
client if the echo element
attempts to echo an undefined variable. This overrides any SSIUndefinedEcho directives.

<!--#config echomsg="[Value Undefined]" -->

errmsg

The value is a message that is sent back to the
client if an error occurs while parsing the
document. This overrides any SSIErrorMsg directives.

<!--#config errmsg="[Oops, something broke.]" -->

sizefmt

The value sets the format to be used when displaying
the size of a file. Valid values are bytes
for a count in bytes, or abbrev for a count
in Kb or Mb as appropriate, for example a size of 1024 bytes
will be printed as "1K".

<!--#config sizefmt="abbrev" -->

timefmt

The value is a string to be used by the
strftime(3) library routine when printing
dates.

This command prints one of the include
variables defined below. If the variable is unset, the result is
determined by the SSIUndefinedEcho directive. Any dates printed are
subject to the currently configured timefmt.

Attributes:

var

The value is the name of the variable to print.

decoding

Specifies whether Apache should strip an encoding from
the variable before processing the variable further. The default
is none, where no decoding will be done. If set to
url, then URL decoding (also known as %-encoding;
this is appropriate for use within URLs in links, etc.) will be
performed. If set to urlencoded,
application/x-www-form-urlencoded compatible encoding (found in
query strings) will be stripped. If set to base64,
base64 will be decoded, and if set to entity, HTML
entity encoding will be stripped. Decoding is done prior to any
further encoding on the variable. Multiple encodings can be
stripped by specifying more than one comma separated encoding.
The decoding setting will remain in effect until the next decoding
attribute is encountered, or the element ends.

The decoding attribute must precede the
corresponding var attribute to be effective.

encoding

Specifies how Apache should encode special characters
contained in the variable before outputting them. If set
to none, no encoding will be done. If set to
url, then URL encoding (also known as %-encoding;
this is appropriate for use within URLs in links, etc.) will be
performed. If set to urlencoded,
application/x-www-form-urlencoded compatible encoding will be
performed instead, and should be used with query strings. If set
to base64, base64 encoding will be performed. At
the start of an echo element, the default is set to
entity, resulting in entity encoding (which is
appropriate in the context of a block-level HTML element,
e.g. a paragraph of text). This can be changed by adding
an encoding attribute, which will remain in effect
until the next encoding attribute is encountered or
the element ends, whichever comes first.

The encoding attribute must precede the
corresponding var attribute to be effective.

In order to avoid cross-site scripting issues, you should
always encode user supplied data.

Example

The exec command executes a given shell command or
CGI script. It requires mod_cgi to be present
in the server. If OptionsIncludesNOEXEC is set, this command is completely
disabled. The valid attributes are:

cgi

The value specifies a (%-encoded) URL-path to
the CGI script. If the path does not begin with a slash (/),
then it is taken to be relative to the current
document. The document referenced by this path is
invoked as a CGI script, even if the server would not
normally recognize it as such. However, the directory
containing the script must be enabled for CGI scripts
(with ScriptAlias
or OptionsExecCGI).

The CGI script is given the PATH_INFO and query
string (QUERY_STRING) of the original request from the
client; these cannot be specified in the URL path. The
include variables will be available to the script in addition to
the standard CGI environment.

Example

<!--#exec cgi="/cgi-bin/example.cgi" -->

If the script returns a Location: header instead of
output, then this will be translated into an HTML anchor.

The include virtual
element should be used in preference to exec cgi. In
particular, if you need to pass additional arguments to a CGI program,
using the query string, this cannot be done with exec
cgi, but can be done with include virtual, as
shown here:

<!--#include virtual="/cgi-bin/example.cgi?argument=value" -->

cmd

The server will execute the given string using
/bin/sh. The include variables are available to the command, in addition
to the usual set of CGI variables.

The use of #include virtual is almost always prefered to using
either #exec cgi or #exec cmd. The former
(#include virtual) uses the standard Apache sub-request
mechanism to include files or scripts. It is much better tested and
maintained.

In addition, on some platforms, like Win32, and on unix when
using suexec, you cannot pass arguments
to a command in an exec directive, or otherwise include
spaces in the command. Thus, while the following will work under a
non-suexec configuration on unix, it will not produce the desired
result under Win32, or when running suexec:

This command prints the size of the specified file, subject
to the sizefmt format specification. Attributes:

file

The value is a path relative to the directory
containing the current document being parsed.

This file is <!--#fsize file="mod_include.html" --> bytes.

The value of file cannot start with a slash
(/), nor can it contain ../ so as to
refer to a file above the current directory or outside of the
document root. Attempting to so will result in the error message:
The given path was above the root path.

virtual

The value is a (%-encoded) URL-path. If it does not begin with
a slash (/) then it is taken to be relative to the current document.
Note, that this does not print the size of any CGI output,
but the size of the CGI script itself.

This command inserts the text of another document or file
into the parsed file. Any included file is subject to the usual
access control. If the directory containing the parsed file has
OptionsIncludesNOEXEC set, then only documents with a text
MIME-type (text/plain,
text/html etc.) will be included. Otherwise CGI
scripts are invoked as normal using the complete URL given in
the command, including any query string.

An attribute defines the location of the document, and may
appear more than once in an include element; an inclusion is
done for each attribute given to the include command in turn.
The valid attributes are:

file

The value is a path relative to the directory
containing the current document being parsed. It cannot
contain ../, nor can it be an absolute path.
Therefore, you cannot include files that are outside of the
document root, or above the current document in the directory
structure. The virtual attribute should always be
used in preference to this one.

The value is a (%-encoded) URL-path. The URL cannot contain a
scheme or hostname, only a path and an optional query string. If it
does not begin with a slash (/) then it is taken to be relative to the
current document.

A URL is constructed from the attribute, and the output the
server would return if the URL were accessed by the client is
included in the parsed output. Thus included files can be nested.

If the specified URL is a CGI program, the program will be
executed and its output inserted in place of the directive in the
parsed file. You may include a query string in a CGI url:

<!--#include virtual="/cgi-bin/example.cgi?argument=value" -->

include virtual should be used in preference
to exec cgi to include the output of CGI programs
into an HTML document.

If the KeptBodySize
directive is correctly configured and valid for this included
file, attempts to POST requests to the enclosing HTML document
will be passed through to subrequests as POST requests as well.
Without the directive, all subrequests are processed as GET
requests.

onerror

The value is a (%-encoded) URL-path which is shown should a
previous attempt to include a file or virtual attribute failed.
To be effective, this attribute must be specified after the
file or virtual attributes being covered. If the attempt to
include the onerror path fails, or if onerror is not specified, the
default error message will be included.

Example

Specifies whether Apache should strip an encoding from
the variable before processing the variable further. The default
is none, where no decoding will be done. If set to
url, urlencoded, base64
or entity, URL decoding,
application/x-www-form-urlencoded decoding, base64 decoding or HTML
entity decoding will be performed respectively. More than one
decoding can be specified by separating with commas. The decoding
setting will remain in effect until the next decoding attribute
is encountered, or the element ends. The decoding
attribute must precede the corresponding
var attribute to be effective.

encoding

Specifies how Apache should encode special characters
contained in the variable before setting them. The default is
none, where no encoding will be done. If set to
url, urlencoding, base64
or entity, URL encoding,
application/x-www-form-urlencoded encoding, base64 encoding or
HTML entity encoding will be performed respectively. More than
one encoding can be specified by separating with commas. The
encoding setting will remain in effect until the next encoding
attribute is encountered, or the element ends. The
encoding attribute must precede the
corresponding var attribute to be effective.
Encodings are applied after all decodings have been
stripped.

Example

In addition to the variables in the standard CGI environment,
these are available for the echo command, for
if and elif, and to any program
invoked by the document.

DATE_GMT

The current date in Greenwich Mean Time.

DATE_LOCAL

The current date in the local time zone.

DOCUMENT_NAME

The filename (excluding directories) of the document
requested by the user.

DOCUMENT_URI

The (%-decoded) URL path of the document requested by the
user. Note that in the case of nested include files, this is
not the URL for the current document. Note also that
if the URL is modified internally (e.g. by an alias or directoryindex), the modified
URL is shown.

LAST_MODIFIED

The last modification date of the document requested by
the user.

QUERY_STRING_UNESCAPED

If a query string is present, this variable contains the
(%-decoded) query string, which is escaped for shell
usage (special characters like & etc. are
preceded by backslashes).

Variable substitution is done within quoted strings in most
cases where they may reasonably occur as an argument to an SSI
directive. This includes the config,
exec, flastmod, fsize,
include, echo, and set
directives. If SSILegacyExprParser is set to on,
substitution also occurs in the arguments to conditional operators.
You can insert a literal dollar sign into the string using backslash
quoting:

<!--#set var="cur" value="\$test" -->

If a variable reference needs to be substituted in the
middle of a character sequence that might otherwise be
considered a valid identifier in its own right, it can be
disambiguated by enclosing the reference in braces,
a la shell substitution:

<!--#set var="Zed" value="${REMOTE_HOST}_${REQUEST_METHOD}" -->

This will result in the Zed variable being set
to "X_Y" if REMOTE_HOST is
"X" and REQUEST_METHOD is
"Y".

The if element works like an if statement in a
programming language. The test condition is evaluated and if
the result is true, then the text until the next elif,
else or endif element is included in the
output stream.

The elif or else statements are used
to put text into the output stream if the original
test_condition was false. These elements are optional.

The endif element ends the if element
and is required.

test_condition is a boolean expression which follows the
ap_expr syntax. The syntax can be changed
to be compatible with Apache HTTPD 2.2.x using SSILegacyExprParser.

The SSI variables set with the var element are exported
into the request environment and can be accessed with the
reqenv function. As a short-cut, the function name
v is also available inside mod_include.

The below example will print "from local net" if client IP address
belongs to the 10.0.0.0/8 subnet.

true if the URL represented by the string is accessible by
configuration, false otherwise. This is useful where content on a
page is to be hidden from users who are not authorized to view the
URL, such as a link to that URL. Note that the URL is only tested
for whether access would be granted, not whether the URL exists.

Example

Compare string1 with string2. If
string2 has the form /string2/
then it is treated as a regular expression. Regular expressions are
implemented by the PCRE engine and
have the same syntax as those in perl
5. Note that == is just an alias for =
and behaves exactly the same way.

If you are matching positive (= or ==), you
can capture grouped parts of the regular expression. The captured parts
are stored in the special variables $1 ..
$9. The whole string matched by the regular expression is
stored in the special variable $0

The boolean operators && and ||
share the same priority. So if you want to bind such an operator more
tightly, you should use parentheses.

Anything that's not recognized as a variable or an operator
is treated as a string. Strings can also be quoted:
'string'. Unquoted strings can't contain whitespace
(blanks and tabs) because it is used to separate tokens such as
variables. If multiple strings are found in a row, they are
concatenated using blanks. So,

string1string2 results in string1string2

and

'string1string2' results in string1string2.

Optimization of Boolean Expressions

If the expressions become more complex and slow down processing
significantly, you can try to optimize them according to the
evaluation rules:

Expressions are evaluated from left to right

Binary boolean operators (&& and ||)
are short circuited wherever possible. In conclusion with the rule
above that means, mod_include evaluates at first
the left expression. If the left result is sufficient to determine
the end result, processing stops here. Otherwise it evaluates the
right side and computes the end result from both left and right
results.

Short circuit evaluation is turned off as long as there are regular
expressions to deal with. These must be evaluated to fill in the
backreference variables ($1 .. $9).

If you want to look how a particular expression is handled, you can
recompile mod_include using the
-DDEBUG_INCLUDE compiler option. This inserts for every
parsed expression tokenizer information, the parse tree and how it is
evaluated into the output sent to the client.

Escaping slashes in regex strings

All slashes which are not intended to act as delimiters in your regex must
be escaped. This is regardless of their meaning to the regex engine.

The SSIErrorMsg directive changes the error
message displayed when mod_include encounters an
error. For production servers you may consider changing the default
error message to "<!-- Error -->" so that
the message is not presented to the user.

This directive has the same effect as the <!--#config
errmsg=message --> element.

Under normal circumstances, a file filtered by mod_include
may contain elements that are either dynamically generated, or that may
have changed independently of the original file. As a result, by default
the server is asked not to generate an ETag header for the
response by adding no-etag to the request notes.

The SSIETag directive suppresses this
behaviour, and allows the server to generate an ETag header.
This can be used to enable caching of the output. Note that a backend server
or dynamic content generator may generate an ETag of its own, ignoring
no-etag, and this ETag will be passed by
mod_include regardless of the value of this setting.
SSIETag can take on the following values:

off

no-etag will be added to the request notes, and the server
is asked not to generate an ETag. Where a server ignores the value of
no-etag and generates an ETag anyway, the ETag will be
respected.

on

Existing ETags will be respected, and ETags generated by the server will
be passed on in the response.

Under normal circumstances, a file filtered by mod_include
may contain elements that are either dynamically generated, or that may
have changed independently of the original file. As a result, by default
the Last-Modified header is stripped from the response.

The SSILastModified directive overrides this
behaviour, and allows the Last-Modified header to be respected
if already present, or set if the header is not already present. This can
be used to enable caching of the output. SSILastModified
can take on the following values:

off

The Last-Modified header will be stripped from responses,
unless the XBitHack directive
is set to full as described below.

on

The Last-Modified header will be respected if already
present in a response, and added to the response if the response is a
file and the header is missing. The
SSILastModified directive
takes precedence over XBitHack.

As of version 2.3.13, mod_include has switched to the
new ap_expr syntax for conditional expressions
in #if flow control elements. This directive allows to
switch to the old syntax which is compatible
with Apache HTTPD version 2.2.x and earlier.

The XBitHack directive controls the parsing
of ordinary html documents. This directive only affects files associated
with the MIME-typetext/html. XBitHack can take on the following values:

off

No special treatment of executable files.

on

Any text/html file that has the user-execute bit
set will be treated as a server-parsed html document.

full

As for on but also test the group-execute bit.
If it is set, then set the Last-modified date of the
returned file to be the last modified time of the file. If
it is not set, then no last-modified date is sent. Setting
this bit allows clients and proxies to cache the result of
the request.

Note

You would not want to use the full option, unless you assure the
group-execute bit is unset for every SSI script which might #include a CGI or otherwise produces different output on
each hit (or could potentially change on subsequent requests).

Notice:This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our mailing lists.